The K01 award will transition Dr. Harry Gill from a currently mentored Assistant Professor to an independent scientific investigator, focusing on understanding the mechanism of Na/HCO3 cotransport by renal NBCe1-A. Dr. Gill's background is in molecular biology, biochemistry, and crystallography. However, because the necessary functional assays are physiological, it is critical that Dr. Gill be integrated into the Physiology Lab of his mentor, Professor Walter Boron. A mentoring committee consisting of senior investigators from three institutions will guide Dr. Gill's progress. The training activities include: (a) developing new experimental (electrophysiological) techniques at the cellular level; (b) preparing for new experimental work at the whole-animal level; (c) taking didactic physiology coursework; (d) performing original research; (e) participating in lab meetings, journal clubs, and seminars; (f) attending mentor at physiologically oriented scientific meetings with mentor; (g) initiating mentor-generated networking; (h) teaching (limited) to enhance training; (i) mentoring undergraduate students in the Lab; and (j) training in grant writing. Item (d) will provide Dr. Gill with preliminary data and otherwise prepare him for his first R01 application. The specific aims of the research plan are: (1) To use X-ray crystallography to illuminate the role of the cytosolic N terminus (Nt) and the human R298S mutation in the function of NBCe1-A. (2) To develop electrophysiological skills as a cell physiologist, and exploit the inside-out giant patch to measure for the first time the dependence of NBCe1-A on cytosol-side [Na], [HCO3], and pH. (3) To explore the functional significance of conduits that appear to weave through the interior of the cytosolic Nt of NBCe1, and to prepare a targeting vector for the future generation of a knock-in mouse carrying a key Nt mutation. The proposed experimental work-from the atomic to the cellular/molecular levels-will provide important new insights into the role of the cytosolic Nt in the function of members of the broader SLC4 family. The K01 training program will produce a well rounded academic scientist who will be highly competitive in submitting his own R01 grant.